The VetRX will help with breathing at the least. If one of mine gets and discharge form it's nose, I isolate and treat it with that for a week, if it doesn't improve, it's culled. I cull about 5% of the ones I treat like that, the rest stop the discharge and sneezing and, after a second week isolate w/o treatment and no symptoms, back to the general population barn.
If the rabbit is not is severe distress, I'd bet the cause is feed dust is all, or there is actually a clear to white discharge being stained by feed. Green to yellow is usually bad enough that the rabbit is obviously in distress and should be culled immediately.